In the prior art, a vehicle is provided with a prime mover to generate a drive force for running, and output of the prime mover is transmitted to wheels through a power transmission system. This power transmission system comprises a clutch, a transmission, a forward/backward switching mechanism and so on. A type and an arrangement of those elements are determined depending on a specification of the vehicle such as a performance etc. One example of the vehicle having the power transmission system of this kind is disclosed in Japanese Patent Laid-Open No. 2001-323978. According to by this Laid-Open, the vehicle is provided with an engine as a prime mover, and a forward/backward switching mechanism, a belt-type continuously variable transmission, and a final speed reducing mechanism are arranged in the output side of the engine. This forward/backward switching mechanism has a planetary gear mechanism, a clutch and a brake, and further comprises a hydraulic control unit for controlling engagement/release of the clutch and the brake.
On the other hand, a belt type continuously variable transmission is equipped with a primary pulley and a secondary pulley, and a belt. In the belt type continuously variable transmission, oil pressures of oil chambers of the primary pulley and the secondary pulley are controlled by a hydraulic control unit. Moreover, a torque converter and a lockup clutch are arranged in parallel on the power transmission route between a crankshaft of an engine and an input shaft connected with the forward/backward switching mechanism. This torque converter comprises a pump impeller connected with the crankshaft, and a turbine runner communicated with the input shaft. The amount of oil fed to the torque converter and the engaging pressure of the lockup clutch are also controlled by the hydraulic control unit. Moreover, the hydraulic control unit comprises a hydraulic circuit, a solenoid valve, and an oil pump for feeding the oil to the hydraulic circuit is arranged in the hydraulic circuit. This oil pump has a body and a rotor. The body is fixed to the transaxle case, and the rotor is so connected with the pump impeller as to rotate integrally.
With the above-mentioned configuration, the engine power is transmitted to the rotor through the pump impeller, thereby driving the oil pump to discharge the oil. In case the lockup clutch is released, the power is transmitted by a kinetic energy of fluid when the engine power is transmitted to the torque converter. On the other hand, in case the lockup clutch is engaged, the power is transmitted by a frictional force when the engine power is transmitted to the torque converter. The engine power is thus transmitted to the forward/backward switching mechanism. Japanese Patent Laid-Open No. 10-220557 also discloses an example of the power transmission system having the oil pump.
According to the power transmission system disclosed in Japanese Patent Laid-Open No. 2001-323978, the engine power is transmitted to the wheels through the torque converter, the forward/backward switching mechanism, and the belt-type continuously variable transmission. However, on the other hand, it is necessary to provide the power transmission system separately with the oil pump for feeding the oil to the torque converter, the forward/backward switching mechanism, and the belt-type continuously variable transmission. This makes the power transmission system itself or including the peripheral equipments structurally large. Therefore, there is room for improving the vehicle mountability.